Alkane sonochemistry

The chemical effects of high-intensity ultrasound on alkane solutions are reported. Primary products are H₂, CH₄, C₂H₂, and smaller 1-alkenes. Strong similarities to high-temperature (>1200°C) alkane pyrolysis are observed and a radical chain mechansim is proposed. The principal sonochemical process appears to be C-C bond cleavage with secondary abstractions and rearrangements. In order to probe the factors which affect sonochemical yields, we have used two very different chemical dosimeters in alkane solutions: radical trapping by diphenylpicrylhydrazyl and decomposition of Fe(CO)₅. In both cases, good correlation is found between the log of the sonochemical rate and the solvent vapor pressure. This result is justifiable in terms of the cavitation "hot-spot" explanation of sonochemistry. Thus, decreasing solvent vapor pressure increases the intensity of cavitational collapse, the peak temperature reached during such collapse, and, consequently, the rates of sonochemical reactions.